Lim-Seok Kang

Removal of ammonium-N from a recirculation aquacultural system using an immobilized nitrifier

Abstract Various immobilization methods were evaluated for the removal of ammonium-N from recirculating aquacultural water. Ba-alginate, Ca-alginate, carrageenan, and agar beads were prepared with nitrifer consortium from the activated sludge of a sewage treatment facility in Sooyoung, Pusan, South Korea. Batch bioreactor tests for the determination of the effectiveness of the immobilized nitrifier and the optimum hydraulic retention time (HRT) were carried out. The nitrifiers immobilized in Ba-alginate and Ca-alginate showed the most effective nitrification, while those immobilized in the carrageenan and agar beads showed reduced activities. Ninety five percent of the ammonia (20 mg/l) added to the batch bioreactor was nitrified in 6 h when immobilized Ba-alginate or Ca-alginate nitrifiers were used. In order to apply the immobilized nitrifier to an aquaculture facility, a continuous bioreactor was used with synthetic aquacultural water containing 2 mg/l ammonia. Using immobilized Ba-alginate and Ca-alginate beads, 94 and 87% of loaded ammonia were removed with in 3.4 h of HRT, respectively. The amounts of ammonia removal per day were in the range of 2.8–82 g ammonia/m3 per day depending on HRT. The highest ammonia removal rate of 82 g/m3 per day was observed when HRT was 0.3 h (18 min).

Application of Combined Coagulation-Ultrafiltration Membrane Process for Water Treatment

The objectives of this research are to identify the membrane fouling potential due to different fractions of NOM and correlate the physicochemical properties of NOM and membranes with the adsorption of humic substances on membrane and investigate the mechanism of coagulation affecting UF, and find the optimum conditions of the combined of coagulation with UF membrane filtration for NOM removal. For Nakdong river water, the humic acid fraction was the most reactive precursor fraction for the formation of the ratio of THMFP/DOC (STHMFP) and TOXFP/DOC (STOXFP). The result of adsorption kinetics tests showed that hydrophobic organics adsorbed much more quickly than hydrophilic organics on both membranes. Thus, hydrophobic compounds exhibited a preferential adsorption onto membrane. In case of the effect of membrane properties on the adsorption of organic fractions, the adsorption ratio (C1/Ce) was greater for the hydrophobic membrane than for the hydrophilic membrane regardless of the kind of organic fractions. For combined coagulation with membrane process, flux reduction rate showed lower than the UF process alone. Also, the rate of flux decline for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Applying the coagulation process before membrane filtration showed not only reduced membrane fouling, but also improved removal of dissolved organic materials that might otherwise not be removed by the membrane. That is, during the mixing period, substantial changes in particle size distribution occurred under rapid and slow mixing conditions due to the simultaneous formation of microflocs and NOM precipitates. Therefore, combined pretreatment using coagulation (both rapid mixing and slow mixing) improved not only dissolved organic removal efficiency but also DBP (Disinfection By-Product) precursors removal efficiency.

Synthesis and Characterization of Polymeric Inorganic Coagulants for Water Treatment

This research explored the feasibility of preparing and utilizing preformed polymeric solution of Al(III) and Fe(III) as coagulants for water treatment. The differentiation and quantification of hydrolytic Al and Fe species in the coagulants were done by utilizing spectrophotometric method based on the interaction of Al or Fe with ferron as a complexing agent. In addition, 27A1-NMR, FT-IR, and powdered XRD were used to characterize the nature and structure of the hydrolytic species in these coagulants. The properties of the polyaluminum chloride (PAC1) and polymeric iron chloride (PIG) showed that the mass fractions of the maximum polymeric Al produced at r(OH/Al)=2.2 and Fe at r=1.5(OH/Fe) were 85% and 20% of the total aluminum and iron in solution, respectively. Coagulation tests were conducted under various coagulant dosages and pHs for each coagulant prepared. In case of PAC1 coagulants, a coagulation test on Nakdong river waters with three PACls (r=2.0, 2.2, 2.35) showed that the effectiveness of coagulation was in the order, r=2.2>2.0>2.35, corresponding to the order of polymeric aluminum contents. And, for the PIC1 coagulants, the PIC1 of r=1.5 was most effective for the removal of turbidity and TOC from the raw water.

The Removal of Algae by Pre-oxidation

The blue-green algae which caused odor problem in the tap water are difficult to precipitate in sedimentation basin and clogged the filter void rapidly. The studies of this paper were not only oxidation, coagulation and sedimentation processes for effectively removing blue-green algae but yellow clay and polyamine for verification as coagulants aids. The results of this research are summarized as follows: Higher ozone dose(C) and longer contact time(T) were needed for a high degree of removing blue-green algae efficiency. the removal rate of blue-green algae was proportional to the value. The removal percent of chlorophyll-a by sedimentation and filter without pre-ozonation was about 75% but 1 mg/L pre-ozonation could increase the removal percent of chlorophyll-a to 99% and more pre-ozonation could remove completely. Though the removal efficiency of turbidity could increased by high dose of chlorination, the dissolved organic carbon was increased. More chlorine dose from 4 to 10 mg/L dissolved organic carbon was decreased. Using yellow clay as coagulant aids increased density of floc so the settling velocity of floc become rising but polyamine could not increase settling velocity of floc though it could formated large floc.